Apple (AAPL) sold more iPads into sales channels in the second quarter this year than it has ever sold in a single quarter. The 17 million iOS slates Apple shipped last quarter represent more units than any Android tablet has shipped in its entire lifespan, but according to a recent study, it may not have been enough to stop the iPad from losing market share to Android-powered rivals.

Strategy Analytics reported last week that Apple’s share of the global tablet market ticked up to 68% from 62% in the June quarter, but research consultancy Frank N. Magid Associates’s data says otherwise. According to the firm, which recently surveyed 4,734 cell phone and smartphone owners, roughly 50% of people currently own an iPad, down significantly from 72% at last count.

The firm says Amazon’s (AMZN) Kindle Fire tablet made the biggest dent in Apple’s tablet share, skyrocketing to 22% since launching last winter. “That’s what made up the difference,” Tom Godfrey, executive director of mobile strategy at Magid, told The Los Angeles Times.

“We expect to see the iPad as the leader, but with the Surface, Kindle Fire, and Nexus [7] as three solid competitors with significant market share,” Godfrey said, noting that he expects the number of tablet users globally to double from 51 million to 106 million by the end of 2013.